Plasticity is the ability of neurons to change their structure and function in response to stimuli. Morphological plasticity, such as dendritic arborization, appears to be most prominent in young organisms, correlating with the most intense period of learning and brain development. Hibernating animals may be a dramatic exception to this rule. A few studies suggest that both structural and synaptic plasticity are taking place in the adult hibernator to an extent not revealed by any other system. Confirmation of these phenomena and understanding of basic dynamics of this system could prove the hibernator to be an informative model system for studying questions of plasticity, including mechanisms for its regulation in adult mammals. We intend to develop a hibernator, the golden-mantled ground squirrel, as a model system for studying structural and synaptic plasticity in an adult mammal. Several fundamental questions about this system will be addressed. First, to what degree is hibernation-related plasticity demonstrated throughout the brain, and do regional differences in electrical activity during hibernation influence plasticity? What is the time course for these changes throughout the hibernation bout? And last, is this phenomenon dependent upon brain temperature? This proposal will address all three questions using intracellular Lucifer Yellow injections and synaptic marker immunofluorescence. Studying neural plasticity in adulthood has far-reaching consequences for medicine. The discovery of mechanisms underlying adult neural plasticity has the potential to progress current treatments of neurodegenerative disorders such as Alzheimer's and Parkinson's diseases, and acute traumatic and ischemic insults.